During stimulation (such as hydraulic fracturing) of a subterranean reservoir, a fluid is pumped into the well which penetrates the reservoir at a pressure which is sufficient to create or enlarge a fracture within the reservoir. During fracturing, vertical fracture faces are held apart by the pumping of pressurized fluid. However, when the treatment ends and the hydraulic pressure is no longer present, the fracture opening closes under the influence of tectonic stresses.
Productivity of a hydraulic fracturing treatment operation is dependent on the effectiveness of the propping agent present in the fracturing fluid within conductive fractures. The proppant serves to prevent the fracture from closing and to hold the faces of the reservoir apart after the pumping treatment is completed and shut-down occurs. The proppant filled fracture increases the effective drainage radius of the wellbore and increases the producing rate of the well.
Pillar fracturing is a known method of creating proppant free channels in-situ wherein separate islands or “pillars” of proppant are created to hold open a fracture with open or conductive areas between the pillars. Proppant pillars formed in-situ conform to the shape and size of the fracture and unpropped areas as then highly conductive channels. Typically, pillar fracturing consists of pumping step-changed stages into a targeted production zone within the well wherein slugs of a clean fluid are followed by a fluid comprising a mixture of clean fluid and proppant. Conventional methods of alternating clean fluid and proppant laden fluid often result however in a gradual transition of clean fluid and proppant laden fluid rather than the desired sharp step-change.
Often conventional processes of pillar fracturing require the use of hindered settling aids, such as fibers, polymers, or surface bonding agents added to the proppant from within the carrier fluid in order to reinforce and consolidate the proppant in-situ and to inhibit settling of the proppant in the treatment fluid. Typically, the fibers added to both proppant-laden fluid and clean fluid aid to keep discrete proppant pillars intact while also filling the channels between the pillars to help hold the pillars in place. Thus, the fibers inhibit lateral expansion that would otherwise reduce the ultimate height of the pillar. Other processes require adhesive based materials as a settling aid to hold the proppant together in-situ while the fracture closes.
Alternative methods of pillar fracturing are desired. It is desired that such methods be capable of transporting proppant far into the targeted zone of the fracture with a minimum of settling and without requiring the use of hindered settling aids. In addition, alternative methods are desired for creating conductive channels in long fracture lengths which do not result in the transitioning of clean fluid and proppant laden fluid seen in step-change pillar fracturing. Such alternative pillar fracturing methods need to be less cumbersome and more predictable than the step-change fracturing methods presently practiced.
It should be understood that the above-described discussion is provided for illustrative purposes only and is not intended to limit the scope or subject matter of the appended claims or those of any related patent application or patent. Thus, none of the appended claims or claims of any related application or patent should be limited by the above discussion or construed to address, include or exclude each or any of the above-cited features or disadvantages merely because of the mention thereof herein.